Velocity and mass air flow sensor

Abstract

A mass air flow sensor (10) has a vortex generator (12) positioned in the air flow for generating two streams of vortices. Spaced vortex detectors (20), (22) are each positioned the same distance downstream of vortex generator (12) in one of the two streams of vortices. Vortex detectors (20), (22) are coupled to a differential amplifier (24) which reduces noise signals applied equally to vortex detectors (20), (22) and enhances vortex signals alternately applied to vortex detectors (20), (22).

I claim: 
     
       1. A device for measuring the velocity of a fluid comprising: a vortex generating means positioned in a fluid stream so that a first stream and a second stream of vortices are formed in the wake of said generating means;   a first pitot tube pressure sensor means positioned in said first stream of vortices for sensing and conducting a pressure variation caused by the passage of the vortices;   a second pitot tube pressure sensor means positioned in said second stream of vortices for sensing and conducting a pressure variation caused by the passage of the vortices;   said first pressure sensor means and said second pressure sensor means being positioned substantially the same distance downstream of said vortex generating means;   a differential processing means coupled to said first and second pressure sensor means for inverting the input from one of said first and second pressure sensor means thereby increasing pressure variations between the two and cancelling out pressure variations common to said first and second pressure sensor means;   said differential processing means including a differential microphone having a diaphragm, a first chamber on one side of said diaphragm being coupled to said first pressure sensor means, and a second chamber on the other side of said diaphragm being coupled to said second pressure sensor means;   a threshold detector with an inverting and a non-inverting input coupled to the output of said differential microphone;   said differential microphone being formed of a generally planar piezoelectric material, each side having a conducting means, one conducting means being connected to said inverting input and the other conducting means being connected to said non-inverting input of said threshold detector; and   a polarizing screen adjacennt to and insulated from said diaphragm and a polarizing voltage being applied between said polarizing screen and the adjacent one of said conducting means thereby bowing said diaphragm and producing a bias voltage.   
     
     
       2. A device as recited in claim 1 further comprising a second screen on the opposing side of said diaphragm from said polarizing screen for equalizing frequency response on both sides of said diaphragm.